U.S. patent number 8,173,997 [Application Number 12/067,825] was granted by the patent office on 2012-05-08 for laminated structure, electronic element using the same, manufacturing method therefor, electronic element array, and display unit.
This patent grant is currently assigned to Ricoh Company, Ltd.. Invention is credited to Koei Suzuki, Takanori Tano, Yusuke Tsuda.
United States Patent |
8,173,997 |
Tano , et al. |
May 8, 2012 |
Laminated structure, electronic element using the same,
manufacturing method therefor, electronic element array, and
display unit
Abstract
A disclosed laminated structure includes a substrate; a
wettability varying layer formed on the substrate, the wettability
varying layer including a material whose critical surface tension
is changed by receiving energy; and an electrode layer formed on
the wettability varying layer, the electrode layer forming a
pattern based on the wettability varying layer. The material whose
critical surface tension is changed by receiving energy includes a
polymer including a primary chain and a side chain, the side chain
including a multi-branched structure.
Inventors: |
Tano; Takanori (Kanagawa,
JP), Suzuki; Koei (Kanagawa, JP), Tsuda;
Yusuke (Fukuoka, JP) |
Assignee: |
Ricoh Company, Ltd. (Tokyo,
JP)
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Family
ID: |
39032830 |
Appl.
No.: |
12/067,825 |
Filed: |
July 19, 2007 |
PCT
Filed: |
July 19, 2007 |
PCT No.: |
PCT/JP2007/064628 |
371(c)(1),(2),(4) Date: |
March 24, 2008 |
PCT
Pub. No.: |
WO2008/018296 |
PCT
Pub. Date: |
February 14, 2008 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20090261320 A1 |
Oct 22, 2009 |
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Foreign Application Priority Data
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Aug 7, 2006 [JP] |
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2006-214684 |
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Current U.S.
Class: |
257/40;
257/E27.001; 257/59; 257/72; 257/E51.001 |
Current CPC
Class: |
H01L
51/0529 (20130101); B32B 27/08 (20130101); Y10T
428/24802 (20150115); H01L 51/0545 (20130101) |
Current International
Class: |
H01L
35/24 (20060101) |
Field of
Search: |
;257/40,59,72,E27.001,E51.001 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2003 243660 |
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Aug 2003 |
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JP |
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2004 99874 |
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Apr 2004 |
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JP |
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2004 107625 |
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Apr 2004 |
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JP |
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2004 107651 |
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Apr 2004 |
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JP |
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2005 39086 |
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Feb 2005 |
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JP |
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2005 72200 |
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Mar 2005 |
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JP |
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2005 75962 |
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Mar 2005 |
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JP |
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2006 60113 |
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Mar 2006 |
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JP |
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WO2005/022664 |
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Mar 2005 |
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WO |
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Other References
31p-YY-5 IJ Formation of Organic TFI's Narrow Channel, Using UV
Patterned Alignment Thin Film: The Japan Society of Applied
Physics, The 52.sup.nd Spring Meeting, Meeting Proceedings, p.
1510, 2005 (with English translation). cited by other .
Supplementary European Search Report issued Feb. 3, 2011, in
corresponding European patent application No. 07768480.1, filed
Jul. 19, 2007. cited by other.
|
Primary Examiner: Ho; Anthony
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, L.L.P.
Claims
The invention claimed is:
1. A laminated structure comprising: a substrate; a wettability
varying layer formed on the substrate, the wettability varying
layer including a material whose critical surface tension is
changed by receiving energy; and an electrode layer formed on the
wettability varying layer, the electrode layer forming a pattern
based on the wettability varying layer, wherein the material whose
critical surface tension is changed by receiving energy includes a
polymer having a primary chain and a side chain, the side chain
including a multi-branched structure, and the polymer having the
primary chain and the side chain with the multi-branched structure
includes a polyimide, wherein a thickness of the wettability
varying layer is in a range of 50 nm to 1 .mu.m.
2. The laminated structure according to claim 1, wherein the
multi-branched structure of the side chain in the material whose
critical surface tension is changed by receiving energy includes a
hydrophobic polymer.
3. An electronic element comprising a substrate on which at least a
semiconductor layer, an insulating film layer, and the laminated
structure according to claim 1 are formed.
4. The electronic element according to claim 3, wherein the
semiconductor layer comprises an organic semiconductor
material.
5. The electronic element according to claim 3, further comprising:
a gate insulating film laminated together with the laminated
structure.
6. The electronic element according to claim 3, wherein the
wettability varying layer also acts as the insulating film
layer.
7. The electronic element according to claim 3, wherein the
laminated structure is used for a plurality of the electrode
layers.
8. An electronic element array comprising a plurality of the
electronic elements according to claim 3 arranged on a
substrate.
9. A display unit comprising the electronic element array according
to claim 8.
10. The laminated structure according to claim 1, wherein the
multi-branched structure of the side chain in the material whose
critical surface tension is changed by receiving energy is a
dendrimer structure.
11. The laminated structure according to claim 1, wherein the
multi-branched structure of the side chain in the material whose
critical surface tension is changed by receiving energy is a
hyperbranched structure.
Description
TECHNICAL FIELD
The present invention relates to organic transistors, and more
particularly to a laminated structure suitable for a field-effect
type organic thin-film transistor having an organic semiconductor
layer, an electronic element such as an organic thin-film
transistor using the laminated structure, a manufacturing method
therefor, an electronic element array, and a display unit.
BACKGROUND ART
In recent years and continuing, organic thin-film transistors using
organic semiconductor materials are under intense study. The
advantages of using organic semiconductor materials in transistors
are flexibility, larger areas, simplification of a process due to a
simple layer structure, and an inexpensive manufacturing
device.
Furthermore, a printing method is employed so that manufacturing
costs are significantly reduced compared to conventional Si-based
semiconductor devices. Moreover, thin films and circuits can be
formed simply and conveniently by employing the printing method, a
spin coating method, and a dipping method.
One of the parameters indicating properties of such an organic
thin-film transistor is the Ion/Ioff ratio of electric current. In
an organic thin-film transistor, the electric current (Ids) flowing
between source/drain electrodes in the saturation region can be
expressed by the following formula (1),
.mu..times..times..times..function..times..times. ##EQU00001##
where the field-effect mobility is (.mu.), the capacitance per unit
area of a gate insulating film is
C.sub.in=.epsilon..epsilon..sub.0/d, where .epsilon. is the
relative dielectric constant of the gate insulating film,
.epsilon..sub.0 is the dielectric constant of a vacuum, and d is
the thickness of the gate insulating film, the channel width is
(W), the channel length is (L), the gate voltage is (V.sub.G), and
the threshold voltage is (V.sub.TH).
This formula indicates that, in order to increase the on current,
it is effective to (1) increase the mobility, (2) decrease the
channel length even more, and (3) increase the channel width.
Furthermore, the field-effect mobility is largely dependent on
material properties, and therefore, materials for increasing the
mobility are being developed.
Meanwhile, the channel length results from the element
construction, and therefore, the element construction has been
devised in an attempt to increase the on current.
Generally, the channel length is reduced by reducing the distance
between source/drain electrodes (electrode interval).
Organic semiconductor materials originally do not have high
mobility, and therefore, the channel length is required to be no
more than 10 .mu.m, more preferably 5 .mu.m or less.
One method of accurately setting a short distance between the
source/drain electrodes is photolithography, which is employed in
an Si process, including the following steps. (1) Apply a
photoresist layer on a substrate with a thin-film layer (resist
application). (2) Remove the solvent by heating (prebaking). (3)
Irradiate ultraviolet rays through a hard mask having a pattern
rendered thereon with a laser beam or an electron beam based on
pattern data (exposure). (4) Remove the exposed resist with an
alkaline solution (developing). (5) Harden the resist of the
unexposed part (referred to as pattern part) by heating
(postbaking). (6) Dip into etching liquid or expose to etching gas
to remove the thin-film layer of portions without resist (etching).
(7) Remove the resist with an alkaline solution or an oxygen
radical (resist separation). The aforementioned steps are repeated
each time after a thin-film layer is formed, to thereby complete an
active component. However, the overall costs are increased due to
expensive facilities and a time-consuming process.
Meanwhile, other attempts are being made to form electrode patterns
by a printing method using an inkjet apparatus in order to reduce
the cost.
In inkjet printing, the electrode pattern can be directly rendered,
and therefore, the material utilization rate is high. Thus, the
manufacturing process may be simplified and costs may be reduced.
However, the jetting precision of inkjet printing is limited due to
the difficulty in reducing the amount of jetted ink and machine
errors. Thus, it is difficult to form patterns of 30 .mu.m or less,
and it is impossible to make the electrode interval as short as 5
.mu.m. This means that it is difficult to manufacture a
high-precision device with an inkjet apparatus alone. Accordingly,
some device is necessary to attain high precision. One approach is
to perform work on the surface onto which ink is jetted.
For example, there is a method of using a gate insulating film made
of a material whose critical surface tension (also referred to as
surface free energy) changes by receiving energy such as
ultraviolet rays (see Patent Document 1). Ultraviolet rays are
irradiated through a mask only onto the portions where the
electrodes are supposed to be fabricated, to create high surface
free energy portions on the surface of the insulating film. An
electrode material including water-soluble ink is inkjetted onto
these portions, so that electrodes are fabricated only on the high
energy portions. Accordingly, high-precision electrode patterns can
be formed on the gate insulating film. By employing this method,
even if ink droplets are jetted onto a borderline between the high
surface free energy portion and a low surface free energy portion,
the droplets can move over to the high energy side due to the
difference in energy. As a result, it is possible to create
patterns with uniform lines. This method is advantageous in that an
electrode interval of 5 .mu.m or less can be realized. However,
ultraviolet rays, more specifically, ultraviolet-C rays having a
short wavelength of 300 nm or less are irradiated onto the gate
insulating film, and therefore, the insulating film is affected and
the insulating properties become degraded.
In another example, the gate insulating film is laminated with a
film made of a material whose surface free energy changes by
receiving ultraviolet rays (see Non-patent Literature 1). By the
same method as that of Patent Document 1, portions with different
levels of surface free energy are created on the film by
irradiating ultraviolet rays, and electrode patterns are created by
an inkjet method. The advantage of this technique is that functions
are separated into the layer in which the insulating properties are
retained and the layer in which the surface free energy changes.
However, because ultraviolet rays are irradiated on the gate
insulating film, there still remains the problem that the
insulating film is affected and the insulating properties are
degraded. As a result, gate leakage is increased and it is only
possible to produce a device having a small Ion/Ioff ratio.
Non-patent Literature 1 reports an attempt of mitigating this
problem by increasing the thickness of the gate insulating film
(approximately 1 .mu.m) in order to reduce the amount of
ultraviolet rays being transmitted to the substrate layer. However,
as indicated by formula 1, if the thickness of the gate insulating
film is increased, the extracted current value Ids is decreased. As
a result, it is only possible to produce a device-having a small
Ion/Ioff ratio.
Consequently, it is necessary to increase the applied voltage
V.sub.G in order to increase the Ion/Ioff ratio. As a result, it is
difficult to produce a low power consuming device.
Patent Document 1: Japanese Laid-Open Patent Application No.
2005-310962
Non-patent Literature 1: The Japan Society of Applied Physics, The
52nd Spring Meeting, 2005, Meeting proceedings, p. 1510
As described above, by the method of fabricating portions of high
surface free energy and portions of low surface free energy on a
gate insulating film with ultraviolet rays or electron beams, it is
possible to fabricate high-precision and high-density electrode
patterns that are difficult to fabricate by the conventional
printing method. However, a problem arises in that the insulating
properties of the gate insulating film become degraded by receiving
high energy light beams. Therefore, it is necessary to mitigate the
adverse effects caused by irradiating high energy light beams.
Accordingly, there is a need for a laminated structure, an
electronic element using the same, a manufacturing method therefor,
an electronic element array, and a display unit, in which
insulating properties of a gate insulating film are not degraded
even if high energy light beams are irradiated on the gate
insulating film.
DISCLOSURE OF THE INVENTION
The present invention provides a laminated structure, an electronic
element using the same, a manufacturing method therefor, an
electronic element array, and a display unit in which one or more
of the above-described disadvantages are eliminated.
An embodiment of the present invention provides a laminated
structure including a substrate; a wettability varying layer formed
on the substrate, the wettability varying layer including a
material whose critical surface tension is changed by receiving
energy; and an electrode layer formed on the wettability varying
layer, the electrode layer forming a pattern based on the
wettability varying layer, wherein the material whose critical
surface tension is changed by receiving energy includes a polymer
including a primary chain and a side chain, the side chain
including a multi-branched structure.
An embodiment of the present invention provides a method of
manufacturing a laminated structure, the method including the steps
of forming a high surface energy portion and a low surface energy
portion on a wettability varying layer by applying energy onto the
wettability varying layer in such a manner that critical surface
tension of a material in the wettability varying layer changes; and
forming a conductive layer on the high surface energy portion by
applying a liquid including a conductive material on the high
surface energy portion, wherein the material whose critical surface
tension is changed by receiving the energy includes a polymer
including a primary chain and a side chain, the side chain
including a multi-branched structure.
An embodiment of the present invention provides a method of
manufacturing an electronic element, the method including the steps
of forming a gate electrode; forming a source electrode; forming a
drain electrode; forming a semiconductor layer; and forming an
insulating layer, wherein at least one of the steps of forming the
gate electrode, the source electrode, and the drain electrode
further includes the steps of forming a high surface energy portion
and a low surface energy portion on a wettability varying layer by
applying energy onto the wettability varying layer in such a manner
that critical surface tension of a material in the wettability
varying layer changes; and forming a conductive layer on the high
surface energy portion by applying a liquid including a conductive
material on the high surface energy portion, wherein the material
whose critical surface tension is changed by receiving the energy
includes a polymer including a primary chain and a side chain, the
side chain including a multi-branched structure.
According to one embodiment of the present invention, there are
provided a laminated structure, an electronic element using the
same, a manufacturing method therefor, an electronic element array,
and a display unit in which insulating properties of a gate
insulating film are not degraded even if high energy light beams
are irradiated on the gate insulating film.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional schematic view of a laminated structure
according to an embodiment of the present invention;
FIG. 2 is a graph indicating irradiation amounts of ultraviolet
rays relative to contact angles of a solution including an
electrode material;
FIG. 3 is a schematic diagram of an organic transistor in which a
gate insulating film is laminated in a laminated structure;
FIG. 4 is a schematic diagram of an organic transistor in which a
laminated structure is used for plural electrode layers;
FIGS. 5A, 5B illustrate an example of an electronic element array,
FIG. 5A is a sectional view and FIG. 5B is a plan view illustrating
arrangements of electrodes; and
FIG. 6 is a sectional view of a display unit employing the
electronic element array shown in FIGS. 5A, 5B.
BEST MODE FOR CARRYING OUT THE INVENTION
A description is given, with reference to the accompanying
drawings, of an embodiment of the present invention.
[Laminated Structure]
A description is given of a laminated structure according to an
embodiment of the present invention. FIG. 1 is a sectional
schematic view of a laminated structure 1 according to an
embodiment of the present invention. The laminated structure 1
includes a wettability varying layer 2 acting as the base, which is
formed on a substrate (not shown). The wettability varying layer 2
is made of a material whose critical surface tension is changed by
receiving energy. In the present embodiment, the wettability
varying layer 2 includes portions that differ in at least the
critical surface tension, namely, high surface energy portions 3
with higher critical surface tension and low surface energy
portions 4 with lower critical surface tension. Between the two
high surface energy portions 3 shown in FIG. 1, there are
microscopic gaps that fall in a range of approximately 1 .mu.m
through 5 .mu.m. Conductive layers 5 are formed on the wettability
varying layer 2 at the high surface energy portions 3. A
semiconductor layer 6 is provided on the wettability varying layer
2 in such a manner as to contact at least the low surface energy
portions 4.
[Wettability Varying Layer]
A description is given of the material whose critical surface
tension is changed by receiving energy, which material is included
in the wettability varying layer.
The material whose critical surface tension is changed by receiving
energy, which material is included in the wettability varying layer
of the laminated structure according to an embodiment of the
present invention, has a characteristic of reducing the amount of
irradiated ultraviolet rays.
In general, it is impossible to change the surface free energy
unless high energy light such as ultraviolet rays are irradiated.
Thus, the material whose critical surface tension is changed by
receiving energy, which material is included in the wettability
varying layer of the laminated structure according to an embodiment
of the present invention, is used for reducing the amount of
irradiated ultraviolet rays.
A detailed description is given of the mechanism for changing the
surface free energy by irradiating ultraviolet rays.
When a light beam having a wavelength of 300 nm or less is
irradiated, a C.dbd.O (carbonyl group) included in the high polymer
side chain is photodecomposed, and a radical of C.dbd.O is
generated. Because the radical has high reactivity, it immediately
reacts to moisture included in the atmosphere, thereby generating
COOH (carboxyl group). Due to this carboxyl group, the surface
becomes hydrophilized. Accordingly, by employing this mechanism,
the following molecular design is possible. Specifically, an ester
binding is introduced into part of the side chain having a
water-repellent structure, such as hydrocarbons or hydrogen
fluoride, preferably near the principal chain. That is, the ester
binding is introduced into a part near the principal chain of the
side chain coming out of the principal chain. Beyond this part,
i.e., at parts of the side chain further away from the principal
chain, a long chain including water-repellent groups such as
hydrocarbons or hydrogen fluoride is fabricated. The group can be
another functional group as long as a double binding of the C.dbd.O
is included. A film made of such molecules has a surface that is
water-repellent because the side chain does not break unless
ultraviolet rays are irradiated. When ultraviolet rays are
irradiated, the portion of the ester binding is broken. As a
result, the long chain such as a hydrocarbon chain or a hydrogen
fluoride chain extending therebeyond is broken. Consequently, a
carboxyl group is generated so that the surface becomes
hydrophilized.
In an embodiment of the present invention, in order to improve the
luminous sensitivity, a high polymer including a principal chain
and a side chain with a multi-branched structure is used as the
material whose critical surface tension is changed by receiving
energy.
One ester binding is decomposed by one photon, and therefore, it is
preferable to have two or more hydrocarbon chains or hydrogen
fluoride chains attached to each ester binding, i.e., provide a
multi-branched structure. Accordingly, with a small amount of
irradiating energy, the surface free energy can be largely changed.
The multi-branched structure can be either a dendrimer structure or
a hyperbranched structure; however, a dendrimer structure is more
preferable. A dendrimer structure refers to a structure in which
the chains are branched in a symmetrical manner from a center
molecule. Meanwhile, a hyperbranched structure has various
branching degrees and polymerization degrees resulting from
polymerizing an AB2 type monomer, that is, the chains are branched
randomly. Definitions of a dendrimer structure and a hyperbranched
structure are described in detail in, e.g., "Dedritic high
polymers" edited by Keigo Aoi and Masaaki Kakimoto, published by
NTS Inc.
In the laminated structure according to an embodiment of the
present invention, the material whose critical surface tension is
changed by receiving energy included in the wettability varying
layer is characterized in that insulating properties are retained
even if ultraviolet rays are irradiated.
Typically, the reason why insulating properties are degraded by
receiving ultraviolet rays is that not only the side chain but also
the primary chain is broken by ultraviolet rays. In order to
prevent this, one approach is to introduce into the primary chain,
a group that does not absorb ultraviolet rays (group including a
sigma binding, e.g., a vinyl group or a framework including Si--O
such as siloxane). However, as indicated by properties of
polyvinyl, polyvinyl phenol, or a high polymer with a siloxane
structure, a polymer with such a framework does not have good
insulating properties. Looking at the three-dimensional structure,
the structure is not rigid, and therefore, the packing is poor and
a dense structure cannot be made. Thus, insulating properties
cannot be retained simply by introducing a group that does not
absorb ultraviolet rays into the primary chain. Another approach is
to make the primary chain long (increase the average number of
molecules), so that the primary chain is long enough to retain
insulating properties even after being broken by ultraviolet rays.
However, if the primary chain is made long, i.e., the average
number of molecules is increased, the solubility into solvents is
degraded. As a result, the film formability is degraded. Thus, it
is not possible to simply make the primary chain long or increase
the average number of molecules. Another approach is to introduce a
material with a high absorption coefficient that can absorb
ultraviolet rays well; however, there are no organic materials with
a high absorption coefficient. Thus, the resolution is to make the
film considerably thick or to use an inorganic material (e.g.,
TiO.sub.2) that has a higher absorption coefficient than organic
materials.
In the case of using an inorganic material, the thin film cannot be
formed with the inorganic material alone. Therefore, particles of
the inorganic material need to be dispersed in a polymer. However,
inorganic particles such as TiO.sub.2 can only be made as small as
approximately 1 .mu.m. For this reason, in order to sufficiently
disperse the particles inside a polymer film, the thickness of the
film needs to be several microns. Consequently, the voltage applied
needs to be increased.
Accordingly, in the wettability varying layer of the laminated
structure according to an embodiment of the present invention, a
polyimide framework that has a rigid primary chain is introduced.
Because the polyimide framework has a rigid primary chain, even if
the chain is broken to some degree, the packing between molecules
can be retained. There are two types of polyimide. One type is a
thermosetting type polyimide that is generated by heating polyamic
acid so that dehydration condensation reaction is caused. The other
type is soluble type polyimide that is already dissolved in a
solvent. With the soluble type polyimide (also referred to as
soluble polyimide), a preferable film can be formed by evaporating
the solvent by heat after application. Meanwhile, the thermosetting
type polyimide generally needs to be heated to a high temperature
(200.degree. C. or more), because the dehydration condensation
reaction does not occur unless it is heated to this extent.
Accordingly, the soluble polyimide is preferably employed as the
high polymer including a principal chain and a side chain with a
multi-branched structure used as the material whose critical
surface tension is changed by receiving energy in the wettability
varying layer of the laminated structure, because soluble polyimide
is highly insulating and solvent-resistant without applying high
heat.
The composition of materials of the wettability varying layer 2 is
described in detail with reference to FIG. 1.
The wettability varying layer 2 can be made from one type of
material or two or more types of materials. To form the wettability
varying layer 2 with two or more types of materials, specifically,
a material with high electrical insulating properties is mixed with
a material whose wettability varies greatly. As a result, it is
possible to provide a wettability varying layer 2 with excellent
electric insulating properties and excellent wettability variation
properties. Examples of the material with high electrical
insulating properties are polyimide, polyamide-imide, epoxy,
silsesquioxane, polyvinyl phenol, polycarbonate, fluororesin, and
polyparaxylene. Alternatively, a crosslinking agent can be added to
polyvinyl phenol or polyvinyl alcohol. The material with high
electrical insulating properties preferably has a hydrophobic group
on the side chain. For example, a side chain with a hydrophobic
group is bound directly or via a binding group to a primary chain
having a framework of polyimide, polyimide-amide, or methacrylate.
Examples of the hydrophobic group have end structures such as
--CF.sub.2CH.sub.3, --CF.sub.2CF.sub.3, --CF(CF.sub.3).sub.2, and
--CFH.sub.2. Polyimide with an alkyl side chain is described in
"Development of new polyimide and technology of providing advanced
functions for next-generation electronics and electronic materials"
published by Technical Information Institute Co., Ltd.
It is possible to use a material that varies greatly in wettability
but has problems in terms of film formability, and therefore, the
material can be selected from a wider range of options. For
example, there may be a case where one of the materials varies
greatly in wettability but has high cohesive power, thus degrading
film formability. By mixing this material with another material
having good film formability, the wettability varying layer can be
fabricated easily.
As described above, the wettability varying layer 2 is made of a
material whose critical surface tension is changed by receiving
energy such as heat, ultraviolet rays, electron beams, and plasma.
Preferably, the amount of critical surface tension is changed
greatly before and after applying the energy. On such a material,
energy is applied to parts of the wettability varying layer 2 in
such a manner as to form patterns with different levels of critical
surface tension, i.e., the high surface energy portion 3 and the
low surface energy portion 4. Thus, liquid including a conductive
material easily adheres to the high surface energy portion 3
(lyophilic) but does not easily adhere to the low surface energy
portion 4 (lyophobic). Accordingly, liquid including the conductive
material selectively adheres to the lyophilic high surface energy
portion 3 in accordance with the pattern shapes, and the adhered
liquid is solidified, thereby forming the conductive layers 5.
The thickness of the wettability varying layer 2 according to an
embodiment of the present invention preferably falls in a range of
30 nm through 3 .mu.m, more preferably in a range of 50 nm through
1 .mu.m. If the wettability varying layer 2 is any thinner,
properties as a bulk body are degraded (insulating properties, gas
barrier properties, and moisture barrier properties). If the
wettability varying layer 2 is any thicker, the surface shape is
degraded.
A description is given of the gate insulating film and the
laminated structure.
The gate insulating film and the laminated structure are laminated
together; however, if the wettability varying layer 2 has good
insulating properties, the wettability varying layer 2 can also act
as the gate insulating film.
If so, the gate insulating film can be omitted.
If both the gate insulating film and the laminated structure are
provided, the wettability varying layer 2 is preferably made of a
material that has a higher absorption coefficient than that of a
material forming a high insulating layer, in order to prevent an
adverse effect caused by irradiating ultraviolet rays.
The gate insulating film is made of a material with higher
insulating properties than that of the wettability varying layer
2.
If insulating properties are higher, it means that the volume
resistance is greater.
If a wettability control layer is laminated on a high insulating
layer, and the wettability control layer contacts the source/drain
electrodes, there can be three or more layers provided. A high
insulating layer can also act as the wettability control layer.
A description is given of the materials of the gate insulating
film.
The insulating film can be made of materials such as polyimide,
polyamide-imide, epoxy, silsesquioxane, polyvinyl phenol,
polycarbonate, fluororesin, and polyparaxylene.
[Multi-Branched Structure]
According to an embodiment of the present invention, the side chain
can include the following multi-branched structure. The alkyl long
chain and the hydrogen fluoride long chain can be molecule chains
other than the examples below. The multi-branched structure can be
any structure other than the examples below.
In the following chemical structural formulae 1 through 8, n is an
integer number 2 through 16. In consideration of solubility into
solvents, n is particularly preferably 4 through 12.
The long chain is of a first generation in the example below;
however, the long chain can be of a second generation or more as
indicated in the chemical structural formulae 5 through 8.
##STR00001## ##STR00002##
[Soluble Polyimide]
In order to perform the film formation process at a low
temperature, the high polymer material having a hydrophobic group
in the side chain preferably includes soluble polyimide. Soluble
polyimide is polyimide that is soluble into a solvent. Soluble
polyimide is made by performing in advance a chemical imidization
process on polyamic acid in a solution. The polyamic acid is
obtained by making polyamic acid dianhydride react with diamine,
which are the materials. If the polyimide framework has a rigid
structure, it does not easily dissolve in a solvent. Accordingly,
in order to disrupt the crystallinity of the polyimide and to
facilitate dissolution, an alicyclic cyclocarboxylic dihydrate
having a high height is generally used.
It is possible to estimate the type of acid anhydride included in
polyimide by analyzing the oscillation of a characteristic group
caused by the infrared absorption spectral properties of the
polyimide thin film and/or by measuring the ultraviolet-visible
absorption spectral properties. A polyimide thin film including
alicyclic cyclocarboxylic dihydrate having a high height would have
an absorption edge wavelength of 300 nm or less. Details are
described in "Latest Polyimide--Basics and Application--" written
by Toshio Imai and Rikio Yokota, edited by Japan Polyimide
Association, published by NTS Inc. in 2002, and "Development of new
polyimide and technology of providing advanced functions for
next-generation electronics and electronic materials" published by
Technical Information Institute Co., Ltd. in 2003.
Because polyimide is dissolved in a solvent, film formation is
possible at a low temperature of 200.degree. C. or less, which is
the temperature at which a solvent evaporates. Furthermore,
unreacted polyamic acid does not remain in the polyimide thin film
or a side reaction product such as acid anhydride does not remain
in the polyimide. This mitigates failures in electric properties of
the polyimide film caused by such impurities.
Soluble polyimide is not soluble in all solvents; it is only
soluble in solvents with high polarity such as .gamma.-butyl
lactone, N-methylpyrrolidone, and N,N-dimethylacetamide.
Accordingly, by forming a semiconductor layer on the wettability
varying layer 2 with a solvent with low polarity such as toluene,
xylene, acetone, and isopropyl alcohol, it is possible to prevent
the thin film including soluble polyimide from being eroded by the
solvent.
In a case of forming the wettability varying layer 2 with two or
more types of materials, the material other than soluble polyimide
having a hydrophobic group in the side chain is also preferably a
soluble material. Accordingly, film formation is possible under low
temperature. Furthermore, the material preferably indicates good
compatibility with soluble polyimide. Accordingly, phase separation
in a solvent can be mitigated, and the materials are optimum for
the film formation process.
The soluble material need not be organic; the soluble material can
be a compound including organic and inorganic substances. Examples
are phenolic resin such as polyvinyl phenol, melamine resin,
polysaccharide such as pullulan treated by an acetylation process,
and silsesquioxane.
Furthermore, if the material other than soluble polyimide having a
hydrophobic group in the side chain also includes soluble
polyimide, it is preferable in terms of heat resistance, solvent
resistance, and affinity.
[Electrode Layer (Conductive Layer)]
The electrode layer (conductive layer) 5 is made by solidifying
liquid preferably including a conductive material by applying heat
or irradiating ultraviolet rays. The liquid including a conductive
material refers to any of the following.
1. Conductive material is dissolved in a solvent.
2. Precursor of conductive material or precursor dissolved in a
solvent.
3. Particles of conductive material are dispersed in a solvent.
4. Precursor particles of conductive material are dispersed in a
solvent.
More specific examples are metal microparticles such as Ag, Au, or
Ni dispersed in an organic solvent or water, or a solution of a
conductive polymer such as doped PANI (polyaniline) or PSS
(polystyrene sulfonate) doped in PEDOT
(polyethylenedioxythiophene).
Examples of a method of applying liquid including a conductive
material on the surface of the wettability varying layer 2 are a
spin coating method, a dip coating method, a screen printing
method, an offset printing method, and an inkjet method. However,
to make more use of the effects of the surface energy on the
wettability varying layer 2, the inkjet method is particularly
preferable because small liquid droplets can be supplied. As
described above, when a head that is typically used in a printer is
employed in the inkjet method, the resolution is approximately 30
.mu.m and the alignment precision is around .+-.15 .mu.m. However,
by making use of the difference in surface energy on the
wettability varying layer 2, it is possible to form finer
patterns.
[Semiconductor Layer]
The semiconductor layer 6 can include an inorganic semiconductor or
an organic semiconductor. Examples of an inorganic semiconductor
are CdSe, CdTe, and Si. Examples of an organic semiconductor are
organic low molecules such as pentacene, anthracene, tetracene, and
phthalocyanine; polyphenylene-based conductive high polymers such
as a polyacethylene-based conductive high polymer,
polyparaphenylene and a derivative thereof, and polyphenylene
vinylene and a derivative thereof; heterocyclic series conductive
high polymers such as polypyrrole and a derivative thereof,
polythiophene and a derivative thereof, and polyfuran and a
derivative thereof; and an ionic conductive high polymer such as a
polyaniline and a derivative thereof. By employing an organic
semiconductor as described above, effects of properties of the
wettability varying layer 2 can be enhanced more significantly.
PRACTICAL EXAMPLES
The following practical examples are for specifically describing
the present invention; however, the present invention is not
limited to these practical examples.
Practical Example 1
In practical example 1, it was confirmed that in a film made from a
dendrimer material, a dendrimer was present, and that the surface
free energy can be changed by irradiating less ultraviolet rays
compared to conventional materials.
First, it was confirmed that a dendrimer was present in the film
formed by applying the material.
A polyimide material (polyimide A) having a dendrimer in the side
chain and a solution of polyimide (polyimide B) without a dendrimer
were respectively applied on glass substrates by a spin coating
method. Next, the substrates were heated in an oven at a
temperature of 180.degree. C., and the solvents were removed. The
resultant film thicknesses were measured with a sensing pin, and
both were 100 nm. A portion of each of the films was scraped off
and dissolved into CDCl3 that is an isotope of chloroform. Then,
the 1H-NMR was measured.
Upon comparing the resultant chart with that of polyimide A that is
the material, it was found that they were substantially the same.
This means that the dendrimer structure remained without being
decomposed even after heating the applied film.
Furthermore, when the scraped off part of the film was put into a
thermogravimetric analyzer, it was confirmed that the weight
changed rapidly (approximately 20% by weight) at approximately
450.degree. C. This value was the same as the proportion of the
dendrimer structure including the hydrocarbon long chain with
respect to the total molecular weight of polyimide A. Accordingly,
it can also be confirmed from this result that the dendrimer
structure is present in the film.
Next, variations in the contact angle with respect to irradiation
of ultraviolet rays were measured.
Ultraviolet rays were irradiated onto each of the films (using an
ultrahigh pressure mercury lamp). The variations in the contact
angle of water and a solution including an electrode material
relative to the irradiation time were measured by a sessile drop
method. The results of the variations in the contact angle of a
solution including an electrode material are shown in FIG. 2.
##STR00003##
These results say that when ultraviolet rays are not irradiated,
the contact angle is larger in polyimide A including a dendrimer
structure than in polyimide B. Similar results were obtained in the
case of pure water.
When ultraviolet rays are irradiated, it was found that the contact
angle in pure water and in a solution with an electrode material
decreases as the exposure amount increases in polyimide A and B. In
the case of the solution with an electrode material, the contact
angle becomes fixed at around 5.degree..
As described above, both in polyimide A that includes a dendrimer
structure and polyimide B, the contact angle changes by irradiating
ultraviolet rays, i.e., the free energy on the film surface
changes. However, in order to attain the same contact angle,
polyimide A requires a significantly smaller amount of ultraviolet
rays compared to polyimide B, which amount is one quarter of that
required by polyimide B. In this manner, by introducing a dendrimer
structure in the side chain, greater variations in the surface free
energy can be attained with a smaller amount of exposure.
Practical Example 2
Properties of electrode patterning were compared between polyimide
A and polyimide B.
Similarly to practical example 1, polyimide A and polyimide B were
respectively applied onto glass substrates to form thin films
having thicknesses of 100 nm.
Ultraviolet rays were irradiated onto each of the films (using an
ultrahigh pressure mercury lamp) through a line-shaped photomask in
such a manner that the illuminance falls in a range 1 through 15
J/cm.sup.2. Accordingly, portions with high surface energy were
formed on the thin films made of polyimide A and polyimide B. Ink
made of an electrode material was jetted onto the formed portions
having high surface energy by an inkjet method. The electrode
material is a known electrode material; specifically, the ink was
made by dispersing silver nanoparticles in a water-based solution
(hereinafter, "silver nano ink"). The electrode material can be
gold nanoparticles or copper nanoparticles. After baking the thin
films in an oven at 200.degree. C., a metallographic microscope was
used to observe whether lines having intervals of 5 .mu.m were
formed. Results are shown in Table 1.
TABLE-US-00001 TABLE 1 Exposure amount (J/cm.sup.2) 1 2 5 10 15
Polyimide A X .largecircle. .largecircle. .largecircle.
.largecircle. Polyimide B X X X .DELTA. .largecircle. there are
portions where lines are not properly formed
These results correspond to the results obtained by measuring the
contact angles of the solution including an electrode material
relative to the exposure amount of ultraviolet rays. That is, on
the film made of polyimide A, an exposure amount of only 2
J/cm.sup.2 is required to form a surface with a high level of
surface free energy and form electrode lines. Meanwhile, on the
film made of polyimide B, approximately 10 J/cm.sup.2 of
ultraviolet rays need to be irradiated to form a surface with a
high level of energy. Furthermore, the contact angles of the
portions in the film made from polyimide B that are not exposed are
not as large as those in the film made from polyimide A.
Consequently, on the film made from polyimide B, even with an
exposure amount of 10 J/cm.sup.2, a sufficient contrast cannot be
obtained. As a result, there are portions where lines with
intervals of 5 .mu.m are not properly formed on the film made from
polyimide B.
As described above, with polyimide A including a dendrimer
structure in the side chain, it is possible to form electrodes with
a smaller exposure amount compared to polyimide B.
Practical Example 3
An organic transistor was fabricated, in which a gate insulating
film and a laminated structure are laminated together.
A vacuum evaporation method employing a metal mask was performed to
form a film A1 on a glass substrate and fabricate a gate electrode
with a film thickness of 50 nm. The polyimide A film according to
practical example 1 was laminated on a parylene film having a film
thickness of 400 nm to form a laminated insulating film. The film
thickness of the polyimide A film was 100 nm.
Ultraviolet rays (using an ultrahigh pressure mercury lamp) were
irradiated through a photomask at an illuminance of 2 J/cm.sup.2 to
form portions with high surface energy on the gate insulating film.
Silver nanoink was jetted onto these high surface energy portions
by an inkjet method, and the gate insulating film was baked at
200.degree. C. to form a source electrode and a drain electrode
with a distance of 5 .mu.m therebetween, i.e., with a channel
length of 5 .mu.m.
As an organic semiconductor material, triallylamine that is
expressed by the following chemical structural formula II was used,
and film formation was performed by a spin coating method to form
an organic semiconductor layer having a film thickness of 30
nm.
##STR00004##
The resultant organic transistor has a structure as shown in FIG.
3, including a substrate, a gate electrode (A1), a laminated
insulating film (gate insulating film), a source electrode, a drain
electrode, and an organic semiconductor layer.
Comparative Example 1
An organic transistor was fabricated with polyimide B.
In the same manner as the practical example 2, a thin film made of
polyimide B having a thickness of 100 nm was formed on a parylene
film. Subsequently, ultraviolet rays (using an ultrahigh pressure
mercury lamp) were irradiated through a photomask at an illuminance
of 15 J/cm.sup.2 to form portions with high surface energy on the
gate insulating film. Based on the results obtained in the
practical example 2, the irradiation amount was specified as 15
J/cm.sup.2 so that electrode lines can be formed. Silver nanoink
was jetted onto these high surface energy portions by an inkjet
method, and the gate insulating film was baked at 200.degree. C. to
form a source electrode and a drain electrode with a distance of 5
.mu.m therebetween, i.e., with a channel length of 5 .mu.m. Film
formation was performed by a spin coating method using the same
organic semiconductor material as that of the practical example 2
to form an organic semiconductor layer.
[Evaluation of Organic Transistor]
Table 2 indicates the evaluation results of transistor properties
of the practical example 3 and the comparative example 1.
TABLE-US-00002 Transistor made Transistor made from polyimide A
from polyimide B Ion/Ioff ratio 5 digits 3 digits Field-effect 3
.times. 10.sup.-3 cm.sup.2/Vs 3 .times. 10.sup.-4 cm.sup.2/Vs
mobility
These results say that properties of electrode patterning are
favorable in the transistor made from polyimide A, and an organic
transistor having field-effect mobility of 3.times.10.sup.-3
cm.sup.2/V per second was fabricated. This value was comparable to
that of an organic transistor including a source electrode and a
drain electrode made from Au and fabricated by a vacuum evaporation
method through a metal mask.
Meanwhile, the transistor made from polyimide B had a large off
current, and the Ion/Ioff ratio was three digits. The field-effect
mobility was in an order of 10.sup.-4 cm.sup.2/V, which was
approximately two digits smaller than that of polyimide A. It is
presumed that this resulted from the difference in the exposure
amount of ultraviolet rays. That is, with polyimide B, ultraviolet
rays need to be irradiated for a longer time to form source/drain
electrodes, and therefore, it is presumed that the parylene used as
the base was affected.
In this manner, with polyimide A having a dendrimer structure in
the side chain, it is possible to fabricate a transistor with
excellent properties.
Practical Example 4
An organic transistor was fabricated, in which the laminated
structure is used for plural electrode layers.
Polyimide C, expressed by the following chemical structural formula
12, was spin coated onto a film substrate and dried/at 150.degree.
C. to form a thin film.
##STR00005## The thickness was approximately 90 nm. Next,
ultraviolet rays (using an ultrahigh pressure mercury lamp) were
irradiated through a photomask at an illuminance of 2 J/cm.sup.2 to
form portions with high surface energy on the film. Silver nanoink
was jetted onto these high surface energy portions by an inkjet
method, and the film was baked at 150.degree. C. to form a gate
electrode.
Next, a small amount of polyimide D expressed by a chemical
structural formula 13 was mixed with a solution of polyimide E
expressed by a chemical structural formula 14. This mixture was
spin coated onto the film, and the film was dried at 150.degree. C.
to form a gate insulating film having a thickness of 500 nm.
##STR00006## Next, ultraviolet rays (using an ultrahigh pressure
mercury lamp) were irradiated through a photomask at an illuminance
of 0.5 J/cm.sup.2 to form portions with high surface energy on the
gate insulating film. Silver nanoink was jetted onto these high
surface energy portions by an inkjet method, and the gate
insulating film was baked at 150.degree. C. to form a source
electrode and a drain electrode with a distance of 5 .mu.m
therebetween, i.e., with a channel length of 5 .mu.m.
Film formation was performed in the same manner as practical
example 3, using polyimide A expressed by the chemical structural
formula 9 as the organic semiconductor material.
The resultant organic transistor has a structure as shown in FIG.
4, including a substrate, a wettability varying layer, a gate
electrode, a gate insulating film also acting as a wettability
varying layer, a source electrode, a drain electrode, and an
organic semiconductor layer.
There were no problems in forming the gate electrode and the
source/drain electrodes, and a transistor having mobility of
2.times.10.sup.-3 cm.sup.2/Vs was fabricated. This value was
comparable to that of an organic thin film transistor including a
source electrode and a drain electrode made from Au and fabricated
by a vacuum evaporation method through a metal mask.
A device including plural organic transistors was fabricated (see
FIGS. 5A, 5B).
A description is given of the process of fabricating an electronic
element array 51 as shown in FIGS. 5A, 5B.
First, a wettability varying layer 2, and then a gate electrode 42
and a wettability varying layer 2 acting as a gate insulating film
were formed on a film substrate in the same manner as practical
example 4. Subsequently, a source electrode layer 5a and a drain
electrode layer 5b were formed in the same manner as practical
example 4. Finally, a solution in which the laminated structure
(polymer) 1 is dissolved in toluene was used to form the
semiconductor layer 6 in island shapes by a microcontact printing
method.
By performing these steps, the electronic element array 51
including a two-dimensional array of 32.times.32 TFTs (electronic
elements 41) formed on a substrate 7 (inter-element pitch of 500
.mu.m) was fabricated. The average mobility of the plural TFTs
(electronic elements 41) was 1.1.times.10.sup.-3 cm.sup.2/Vs.
Next, a display unit was fabricated (see FIG. 6).
A description is given of the process of fabricating a display unit
61 employing the electronic element array 51 shown in FIGS. 5A,
5B.
To form display elements 64, first, microcapsules 67 including
titanium oxide particles 65 and Isoper 66 colored with oil blue
were mixed in a PVA solution. This was applied onto a polycarbonate
substrate 63 coated with a transparent electrode 62 including ITO,
thereby forming a layer including the microcapsules 67 and a PVA
binder 68. This substrate was bonded together with the substrate 7
on which the TFT array (electronic element array 51) is formed,
which was fabricated in the practical example 4. A driver IC used
for scanning signals was connected to a bus line connected to the
gate electrode 42 and a driver IC used for data signals was
connected to a bus line connected to the source electrode layer 5a.
When the screen was switched every 0.5 seconds, favorable still
images were displayed.
According to one embodiment of the present invention, the process
of manufacturing a laminated structure can be simplified and
performed at a reduced cost.
Further, according to one embodiment of the present invention, an
electronic element such as a thin film transistor with good
properties can be provided.
Further, according to one embodiment of the present invention, the
process of manufacturing an electronic element such as a thin film
transistor can be simplified and performed at a reduced cost.
Further, according to one embodiment of the present invention,
high-precision and high-density electrode patterns can be formed on
all electrode layers in an electronic element such as a thin film
transistor.
Further, according to one embodiment of the present invention, the
process of manufacturing an electronic element array can be
simplified and performed at a reduced cost, and an active matrix
substrate including a low-cost and high-performance organic thin
film transistor can be provided.
Further, according to one embodiment of the present invention, by
combining an active matrix substrate including an organic thin film
transistor with a pixel display element, an inexpensive and highly
flexible display unit can be fabricated.
Further, according to one embodiment of the present invention, a
method can be provided for easily manufacturing a laminated
structure including fine electrode patterns by a low-cost method at
a high material utilization rate, such as a printing method.
Further, according to one embodiment of the present invention, a
method can be provided for manufacturing a laminated structure
including high-precision and high-density electrode patterns.
Further, according to one embodiment of the present invention, a
method can be provided for easily manufacturing a laminated
structure including fine electrode patterns without affecting the
inside of the element.
Further, according to one embodiment of the present invention, an
appropriate method can be provided for manufacturing a laminated
structure, making use of the characteristics of the wettability
varying layer.
Further, according to one embodiment of the present invention, a
method can be provided for easily manufacturing an electronic
element such as a field-effect type transistor including fine
electrode patterns by a low-cost method at a high material
utilization rate, such as a printing method.
Further, according to one embodiment of the present invention, a
method can be provided for manufacturing an electronic element such
as a field-effect type transistor including high-precision and
high-density electrode patterns.
The present invention is not limited to the specifically disclosed
embodiment, and variations and expansions may be made without
departing from the scope of the present invention.
The present application is based on Japanese Priority Patent
Application No. 2006-214684, filed on Aug. 7, 2006, the entire
contents of which are hereby incorporated by reference.
* * * * *